Stroke is the third leading cause of death and disability in the United States. Understanding the molecular mechanisms that lead to neuronal injury and cell death may lead to novel therapeutics to treat this devastating disorder. A variety of studies indices in models of ischemia indicate the involvement of oxygen free radicals, oxidative stress and DNA damage in the pathogenesis of stroke. Preliminary studies indicate a potential pivotal role for Poly (ADP-ribose) polymerase (PARP) in the pathogenesis of stroke. PARP is a ubiquitous and unique protein which is activated by DNA strand nicks and breaks which can be induced by neuronal injury. Activation of PARP may lead to the loss of cellular NAD+ and ATP, resulting in acute cell injury and death. These events may be crucial in both short- and longer-term deleterious effects of stroke. However, it is unclear whether this pathway (PARP activation and NAD+ loss) caused by ischemia is solely responsible for cell death, or whether other pathways such as caspase activation, which involves cleavage of PARP and other substrates may contribute to neuronal injury. Accordingly, this project is designed to explore the molecular mechanisms and consequences of PARP activation and cleavage following excitotoxic neuronal injury, as well as, the molecular consequences of poly PARP activation and cleavage following excitotoxic neuronal injury, as well as, the molecular consequences of poly (ADP-ribosyl)ation of target proteins. In Specific Aim #1 we will determine the role of PARP activation and PARP mediated cell death following excitotoxic (NMDA versus kainate/AMPA) and mitochondrial toxin mediated PARP mediated cell death following excitotoxic injury. In Specific Aim #3 we will examine the role of nitric oxide, superoxide generation and peroxynitrite formation in PARP activation and PARP mediated cell death following excitotoxic (NMDA) mediated neuronal injury. Clarifying and understanding the molecular consequences of PARP activation and caspase cleavage and the role reactive oxidants in this process following excitotoxic neuronal injury may yield important insight into the function of PARP that may identify novel targets for therapy aimed at preserving neurologic function following neuronal injury and stroke.